Standing seam metal roofs are normally manufactured from metal panels of prepainted steel or aluminum. These panels vary from two to three feet in width and twenty to forty feet in length. In constructing a building, the structural walls or columns of the building are first erected and beams, or trusses, forming the primary roof support are carried by the walls of columns of the structure. These trusses usually extend transverse of the length of the building. The trusses in turn support purlins, or joists. Normally, blankets of insulation are spread across the joists, after which the standing seam roof assembly is constructed. The panels are joined to each other along adjacent sides. In the roof of our invention, these sides are lapped together to form standing seams. The roof assembly must be secured to the infrastructure, and this is done by means of clips which prevent the roof from being blown from the structure. Present-day metal roofs have low slopes, their pitch being roughly in the neighborhood of two to five degrees. Standing seams lend stiffness and strength to the roof structure. The metal roof will expand and contract as a function of the coefficient of expansion of the metal of which the roof is made and the temperature cyles to which it is exposed. It is known, in the prior art, to provide sliding clips to allow relative motion between the roof and the infrastructure, thus permitting the roof to "float". The repeated action of expansion and contraction weakens the panel-to-panel-to-lap joint, sometimes causing structural failure and, frequently, leaks. The leaks are caused by the weakening of the fastening means and working or kneading of the sealant used at the joints. In the prior art, the sealant used required adhesion, flexibility, and water-repellency. The design of the joint was such that in many instances the pressure on the sealant varied greatly throughout the length of the sidelap and endlap joints. The endlap joints were normally located in the lowest part of the panel. In such location, water tended to run directly over the joints. Any deterioration of the sealant in these endlap joints would permit wind gusts to drive water into the joints, causing leakage. At numerous places along the roof, there are areas where two end panels and two adjacent side panels form a four-corner intersection. This area is particularly difficult to seal. Watertightness of the roof has been a recurring problem in standing seam roofs. Very frequently, the air in the interior of the building may be conditioned. In the process of doing this, the atmospheric pressure may become greater than the pressure in the building and rain water running over the roof may be sucked through the endlap. The sidelap has water overlying it less frequently.